This invention relates to the use of ultrasonics as a means of cleaning tubulars. The invention provides or an ultrasonic tool that finds one application in the cleaning of down-hole completions. Other applications include production pipelines, sewage pipes, power stations, process facilities, refineries etc.
Herein, references to scale should be construed broadly and other deposits, particles, debris or the like, including for example waxes, grease and ashphaltines, may be substituted as alternatives to this term.
The development of scale in down-hole completions is known to have detrimental implications for the economic prosperity and operating efficiency of a well. Specifically, the collection of scale on a well""s production tubing, casing and perforations serves to impose a constriction on the circulation and production flow paths, thereby limiting production capability. The full extent of the problem may be further realised in light of the additional costs associated with the removal of the scale, together with the loss of production while so doing.
Typically, scale may comprise strontium sulphate (notably a radioactive substance), barium sulphate, calcium carbonate and so on and may result from precipitation of fluids in the well or pipeline. For example, the formation of scale may result from these substances coming out of solution of the production fluid as it undergoes a pressure drop when, such as in an oil well, it passes from the oil reservoir into the well bore via perforations in the production casing. Furthermore, this may be exacerbated as a result of water flooding a reservoir using seawater. Seawater eventually xe2x80x9cbreaks throughxe2x80x9d to the production perforations resulting in the formation of other scales, typically barium sulphate.
The scale, while known to form in the production flow paths, often collects in areas that are difficult to clean or access, such as side pockets, production devices and the perforations in production casing.
In the past a number of alternative methods of removing or mitigating the effect of the formation of scale have been contemplated. In one case, the use of chemicals has been employed; the chemicals being adapted to inhibit the adherence of the scale deposits on the reservoir rock and well tubing. However, a disadvantage associated with this solution is that the chemicals only have a finite life and lose their effectiveness over time, necessitating regular re-application.
Another proposed method involves the use of chemicals in a remedial manner, namely to remove scale that has formed on the tubing. The chemicals, of this type, incorporate dissolving agents to attack the scale deposits. Unfortunately, these chemicals tend to be relatively expensive and slow acting.
Additional, both of the above types of chemicals can be detrimental to the surrounding environment, and usually involve the production or wastage of by-products arising from their manufacture or use, which may be abrasive in the well bore or harmful to the environment upon their disposal. Some of these chemicals are also hazardous to handle and, in this way, further undesirable.
Other methods of attacking or minimising scale involve physical means, but again, operations such as milling or grinding are slow, expensive and not entirely effective. Other physical operations involve bead blasting and have the aforementioned drawbacks with the added difficulty of handling the beads, both before and after use.
It may be seen therefore that until now there has been a lack of an effective or satisfactory system for scale removal in down-hole oil field applications that removes all scale, including the scale formed in remote or difficult areas such as side pockets or perforations, and which does not damage the tubular/cement/formation bond or have a waste by product of its own.
Another desirable attribute of a suitable means or agent for scale removal or prevention is that the means or agent should be deployed using standard running or well equipment.
In the present invention it is understood that the use of ultrasonics may provide an effective method for removing the scale or other matter such as wax or asphaltines.
Ultrasound is highly versatile and can be used in a broad range of applications from medical treatments to chemical transformations.
The effects of ultrasound are achieved by the formation of cavities in the medium through which the ultrasound is used. The formation of the cavities is as a result of the rarefaction of the medium and as a consequence bubbles are formed. Cavitation bubbles are created at sites of rarefaction as the liquid fractures or tears because of the negative pressure of the sound wave in the liquid. As the wave fronts pass, the cavitation bubbles oselate under the influence of positive pressure, eventually growing to an unstable size. Finally, the violent collapse of the cavitation bubbles results in implosions, which cause shock waves to be radiated from the sites of the collapse. The collapse and implosion of meriede cavitation bubbles throughout an ultrasonically activated liquid result in the effect commonly associated with ultrasonics. It has been calculated that temperatures in excess of 10,000 degrees fahrenheit and pressures in excess of 10,000 psi are generated at the implosion sites of cavitation bubbles.
British Patent GB 2 165 330A provides an example of the use of ultrasound as a cleaning system. This system relies on the focussing of the ultrasonic energy using a parabolic curve or a flat array in combination with a focusing means. However, this system would not be suitable for general cleaning operations that require precise focussing of the ultrasonic energy.
It is an object of the present invention to provide an ultrasonic tool that may be used in the cleaning of down-hole completions.
A further object of the invention is to provide an ultrasonic tool that is equally suitable for cleaning well casing, well liner or the well riser, irrespective of varying diameters.
A yet additional and desirable objective would be to provide an ultrasonic tool that, while capable of providing a cleaning function in a oil or gas drilling well, also had the capability of stimulating production by a process of mircofracturing rock formation so as to create additional flow paths in the producing zone. It is intended that the present invention meets this objective.
According to a first aspect or the present invention there is provided apparatus for cleaning tubulars, the apparatus comprising mechanical vibration means for creating acoustic waves, a high frequency current electrical source and a polarisation current source, wherein electrical current generated by the said sources is used to excite or activate the mechanical vibration means.
Preferably the mechanical vibration means is a submersible magnetostriction vibrator.
The apparatus is most typically suitable for cleaning well bore tubulars, and may further comprise an electric conductive wireline cable on which the acoustic vibrator is adapted to be run into the well, wherein the high frequency and polarisation electrical sources are adapted to be positioned at surface, and physically connected to the wireline cable for the conducting of electrical current to the vibrator.
Also according to the first aspect of the present invention there is provided apparatus for cleaning well bore tubulars, the apparatus comprising an ultrasound source suspended on a work string adapted to be run in the well, wherein the ultrasound source provides sufficient ultrasonic energy to remove scale or other undesirable debris or particles from the well bore tubular.
The ultrasound source may be a sonic horn or node. An alternative or additional ultrasound source may also be employed.
The work string may be wireline cable, drill pipe or coil tubing.
The apparatus may further comprise an insulator for preventing the diffusion of sonic energy in a direction up the work string to which the acoustic vibrator may be attached, in use.
The apparatus may further be provided with means for directing the ultrasonic energy; for example one or more nozzles may be incorporated onto the tool and associated with the ultrasound source for the purpose of directing the emitted energy.
Optionally, the apparatus comprises an ultrasound source comprising a body member having an internal profile adapted to manipulate fluid pressure therein. For this reason, the tool may advantageously be provided with a means for regulating the internal pressure. Such means may comprise one or more valves that co-operate to prevent relatively high pressures from migrating back up the tool string. The valves should be provided in sufficient quantity and positioned to enable such pressures to be distributed and to provide back-up in the event of partial failure.
Typically, the profile of the tool body would include convergent and divergent flow paths for the purpose or manipulating and increasing the fluid pressure.
Where, as is preferred, the ultrasound source is a magnetostriction vibrator it may comprise of two blended packages connected by a wave guide means, wherein the blended packages include cores to which excitation and polarisation windings are applied.
According to a second aspect to the present invention there is provided a method for cleaning a tubular, the tubular supporting or containing a fluid, the method comprising the steps of introducing an ultrasound source into the liquid within the tubular and activating same so as to provide ultrasonic energy from the source via the fluid in order to remove scale or other debris or particles from the tubular.
The method may comprise the steps of generating high energy fluid in the ultrasound source, thereby emitting ultrasonic energy from the source via the fluid in order to remove scale from the tubular.
The tubular may be provided in a oil or gas well bore, such as well casing, well liner or well riser. Therefore, the method may further comprise attaching the ultrasound source to a work string and lowering said work string into the well bore.
The method may also involve the adjustment of the output of the tool to achieve the required de-scaling without damaging the down-hole completion.
The method may further involve the recycling of dislodged material through the tool to assist the removal of scale.
Also according to the second aspect of the present invention there is provided a method for cleaning a well bore, the method comprising the steps of activating a submersible magnetostriction vibrator provided on a conductive wireline cable suspended in the well bore by means of surface modules adapted to generate appropriate electrical current to the magnetostriction vibrator via the wireline cable, wherein the said electrical current is converted by the magnetostriction vibrator into. mechanical vibrations adapted to generate ultrasonic energy, and wherein said ultrasonic energy is adapted to clean the well bore tubular.
Preferably also, the activation of the magnetostriction vibrator provides a combined acoustic-thermal effect on the well and any oil therein.
Preferably also, the method comprises a means of cleaning the pores or passageways in the oil bearing layer of the well bore formation.
Preferably also, the method comprises the process of thinning oil in the vicinity of the ultrasound source.